DIAGNOSIS The motor base isn't properly engaging with the jar's drive socket. The most common cause is the silicone gasket in the lid being out of place, which prevents the jar from seating all the way down.
FIX First, unscrew the blade assembly from the jar. Check the black silicone ring (the gasket) that sits around the center post inside the lid. Make sure it's seated flat in its groove, not pinched or folded. Reassemble the blade unit tightly onto the jar. When you place the jar on the base, press down firmly until you hear/feel a distinct click, then press the power button.
IF THAT DIDN'T WORK The issue might be debris like a fruit seed or a bit of frozen fruit jammed between the blades and the housing, physically locking them. Disassemble the blade unit completely and check for any obstructions in the small central well where the blade shaft sits.
HEADS UP The jar must be clicked fully onto the base for the safety interlock to engage. If it's just sitting loosely, you'll only get that empty clicking sound from the motor trying and failing to turn.